If you have already e-filed or mailed the return, you will need to wait until the IRS has accepted that return. Once they accept it and you have received your refund, then you can amend the return to add the additional W-2s. If it gets rejected, you can just make the needed changes and file again.
- After you have received your refund, you can go here https://ttlc.intuit.com/questions/3061514 and get instructions for how to amend the return. Amended returns must be mailed in to address on instructions form.
See some reasons you'd need to amend your return here https://ttlc.intuit.com/questions/1908543